1. Field of the Invention
The present invention relates to a method of manufacturing a silicon optoelectronic device, a silicon optoelectronic device manufactured by the method, and an image input and/or output apparatus having the silicon optoelectronic device.
2. Description of the Related Art
An advantage of using a silicon semiconductor substrate is that it provides excellent reliability and allows highly integrated density of a logic device, an operation device, and a drive device on the substrate. Also, a silicon semiconductor material can be used in fabrication of a highly integrated circuit at much lower cost than a compound semiconductor material, due to the use of inexpensive silicon. That is why many integrated circuits use silicon as their basic material.
In this regard, studies on fabrication of silicon-based light-emitting devices have been continued to compatibly use them in fabrication of integrated circuits and to obtain inexpensive photoelectronic devices. It has been demonstrated that porous silicon and nano-crystal silicon have light emission characteristics.
FIG. 1 depicts the section of a porous silicon region formed at a bulk monocrystalline silicon surface, and an energy band gap between the valence band and the conduction band of the porous silicon region.
Porous silicon is the result of anodic electrochemical dissolution of the surface of bulk monocrystalline silicon, for example, in an electrolyte solution containing a hydrofluoric acid (HF).
When bulk silicon is subjected to anodic electrochemical dissolution in a HF solution, a porous silicon region 70 having numerous pores 70a is formed at the surface of the bulk silicon, as shown in FIG. 1. The pores 70a have more Si—H bonds, relative to intact areas 70b which have not been dissolved by a HF solution. The energy band gap between the valence band energy (Ev) and the conduction band energy (Ec) of the porous silicon region 70 has a shape contrasting to the porous silicon region 70.
Depressions between prominences in energy bands, i.e., the intact areas 70b between the pores 70a in the porous silicon region 70 exhibits a quantum confinement effect. Therefore, the energy band gap of the depression becomes larger than that of the bulk silicon, and electrons and holes are trapped in the intact areas 70b, thereby inducing light-emitting recombination.
For example, in the porous silicon region 70, when the intact areas 70b between the pores 70a are formed in the shape of monocrystalline silicon wires that exhibit a quantum confinement effect, electrons and holes are trapped in the wires, thereby inducing light-emitting recombination. A light-emitting wavelength can vary from a near-infrared light area to a blue light area wavelength according to the sizes (widths and lengths) of the wires. In this case, the period of the pores 70a may be about 5 nm and the maximal thickness of the porous silicon region may be 3 nm, as shown in FIG. 1.
Therefore, when a predetermined voltage is applied to monocrystalline silicon having the porous silicon region 70 in a porous silicon based light-emitting device, light of a predetermined wavelength band can be emitted according to porosity.
However, a porous silicon based light-emitting device as described above does not yet provide reliability as a light-emitting device and exhibits external quantum efficiency (EQE) as low as 0.1%.
FIG. 2 is a schematic sectional view of an example of a nano-crystal silicon light-emitting device.
Referring to FIG. 2, a nano-crystal silicon light-emitting device comprises a stacked structure of a p-type monocrystalline silicon substrate 72, an amorphous silicon layer 73 formed on the substrate 72, an insulator 75 formed on the amorphous silicon layer 73, and lower and upper electrodes 76 and 77 formed on the lower surface of the substrate 72 and the upper surface of the insulator 75, respectively. Nano-crystal silicon quantum dots 74 are formed in the amorphous silicon layer 73.
When the amorphous silicon layer 73 is recrystallized by rapid heat treatment at 700° C. under an oxygen atmosphere, the nano-crystal silicon quantum dots 74 are formed. In this case, the amorphous silicon layer 73 has a thickness of 3 nm and the nano-crystal silicon quantum dots 74 have a diameter of about 2 to 3 nm.
In a light-emitting device using the nano-crystal silicon quantum dots 74 as described above, when a reverse voltage is applied across the upper and lower electrodes 77 and 76, a high electric field is generated at both ends of the amorphous silicon layer between the silicon substrate 72 and the nano-crystal silicon quantum dots 74, thereby generating electrons and holes of high-energy states. Therefore, the tunneling of the generated electrons and holes into the nano-crystal silicon quantum dots 74 occurs, thereby resulting in light-emitting recombination. In this case, a light-emitting wavelength in a light-emitting device using the nano-crystal silicon quantum dots 74 decreases as the sizes of the nano-crystal silicon quantum dots decrease.
However, light-emitting devices using the nano-crystal silicon quantum dots 74 have problems in that it is difficult to control the sizes of the nano-crystal silicon quantum dots and to obtain the uniformity of the nano-crystal silicon quantum dots, and light-emitting efficiency is very low.